Method of assembling electric high-voltage fuses and subassembly therefor

ABSTRACT

A method of assembling high-voltage fuses having a helically wound fusible element which has no supporting mandrel and is maintained in its helical shape by a closely or densely packed pulverulent arc-quenching filler. The method involves the steps of forming a squirrel-cage-like structure by a pair of terminal plugs and a plurality of rods arranged between the pair of terminal plugs, winding the fusible element helically around the rods, inserting the squirrel-cage-like structure with the fusible element wound thereon into a casing, filling a pulverulent arcquenching filler into the casing and removing the rods from the terminal plugs and from the casing by exerting an axial pull upon the rods.

United States Patent Salzer [451 Nov. 12, 1974 METHOD OF ASSEMBLING ELECTRIC HIGH-VOLTAGE FUSES AND The Chase-Shawmut Company, Newburyport, Mass.

Filed: July 9, 1971 Appl. No; 161,089

Assignee:

US. Cl 337/158, 29/623, 337/239, 337/252 Int. Cl. H0lh 85/04 Field of Search 29/614, 623; 337/158, 159, 337/161, 227, 228, 229, 231, 232, 233, 234, 235, 236, 237, 252, 290, 293, 295

References Cited UNITED STATES PATENTS 3,611,238 10/1971 Kozocka 337/159 2,740,187 4/1956 Jacobs, Jr. et a1. 337/228 X FOREIGN PATENTS OR APPLICATIONS 601,752 12/1931 Germany 337/228 Primary Examiner-J. D. Miller Assistant Examiner-Fred E. Bell [57] ABSTRACT A method of assembling high-voltage fuses having a helically wound fusible element which has no supporting mandrel and is maintained in its helical shape by a closely or densely packed pulverulent arc qucnching filler. The method involves the steps of forming a squirrel-cage-like structure by a pair of terminal plugs and a plurality. of rods arranged between the pair of terminal plugs, winding the fusible element helically around the rods, inserting the squirrel-cage-like structure with the fusible element wound thereon into a casing, filling a pulverulent arc-quenching filler into the casing and removing the rods from the terminal plugs and from the casing by exerting an axial pull upon the rods.

15 Claims, 12 Drawing Figures o E i PATENTEWH 21914 A 3.848.214 SHEEI 20$ 3 METHOD OF ASSEMBLING ELECTRIC HIGH-VOLTAGE FUSES AND SUBASSEMBLY THEREFOR BACKGROUND OF THE INVENTION In most high-voltage fuses having a fusible element which is helically wound, the fusible element is supported by an insulating mandrel, e.g., a mandrel of a ceramic material. Other high-voltage fuses having a fusible element which is helically wound do not include such a mandrel. In such fuses the portion of the fusible element between the terminals of the fuse is maintained or supported in its helical form substantially by the pressure of densely packed pulverulent arc-quenching filler by which it is surrounded. Omission of a mandrel for supporting a fusible element is generally desirable. The cost resulting from the omission of a linksupporting insulating mandrel may, however, be quite high, and thus it has been found desirable in many instances to provide, rather than dispense with, a fuselink-supporting mandrel. It is possible to manufacture fuses without link-supporting mandrel if the fusible element is made of resilient silver and forms an extension spring capable of supporting itself. Then the filling of the casing of the fuse must be conducted in such a way as to preclude any distortion of the helically wound fusible element, or fuse link, by the impact upon it of the pulverulent arc-quenching filler. Fuses of this kind which do not include a supporting mandrel for the fusible element are subject to the limitation that thefusible element must have specific mechanical properties. In some instances the requirement in regard to mechanical properties can be met easily, but in other instances such requirement can only be met with difficulty, or not at all.

A prior art method of manufacturing high-voltage fuses having fusible elements which are wound helically, and are only supported by the surrounding arcquenching medium, or quartz sand, to the exclusion of a supporting mandrel includes the following steps. First the fusible element is wound around a mandrel, then the mandrel is placed into the casing of the fuse which has been closed at one end thereof, then the casing is filled with a pulverulent arc-quenching filler and the mandrel is gradually withdrawn from the casing as the latter is gradually filled with the arc-quenching filler. This process requires a great deal of manual dexterity, in particular because of the need to manually maintain the mandrel and the winding in proper relation to the casing, and has been found to be unacceptable were the cost of highly skilled labor is relatively high, and also where particularly thin and relatively fragile fusible elements in form of ribbons are intended to be used. When the temporary mandrel supporting the helically wound fuse link is withdrawn in axial direction from the casing of the fuse, a relatively large void is formed, which is due to the relatively large size of the mandrel. Pulverulent arc-quenching filler present in the space between the casing of the fuse and the mandrel tends to rush into the aforementioned void, and to thereby distort the portion of the fusible element from which the'mandrel support is being withdrawn to be substituted by the pulverulent filler support. In order to minimize the danger of such distortion the mandrel must be removed in very small increments which is one constraint which renders the above referred-to manufacturing process extremely difficult. Another serious limitation of the above-referred-to prior art method of assembly resides in the fact that the support for the helically wound fusible element is not arranged in a fixed coaxial relation to the casing and to the terminal element by which the casing is closed on one side while being filled with a pulverulent arc-quenching filler from the other side. In the above prior art method one terminal element is affixed to the casing prior to filling thereof with a pulverulent arc-quenching filler, and the other terminal element is affixed to the casing after filling thereof with a pulverulent arc-quenching filler. This makes it difficult to establish a conductive connection between one or more helically wound ribbon fuse links and the terminal element to be affixed to the casing only after the latter has been filled with a pulverulent arc-quenching filler.

It is a widely accepted practice in'this country to use a pair of terminal plugs as terminal elements, but the aforementioned prior art assembly does not lend itself to fuse structures having a pair of terminal plugs because it is virtually impossible to establish a conductive connection between the end of a ribbon fuse link adjacent to the open end of the casing and a terminal plug to be press-fitted into that open end.

The invention provides a novel method of assembling high-voltage fuses having a helically wound fusible element which has no supporting mandrel. This method results in fuses not subject to the limitations of some of the above referred-to prior art fuses not requiring a supporting mandrel for their helically wound fusible elements. The method according to this invention, while predicated on a removal of a supporting mandrel for the helically wound fusible element during the process of assembling the fuse, is not subject to the limitations of the above referred-to assembly process wherein the supporting mandrel for the fusible element is removed during the process of assembling the fuse.

SUMMARY OF THE INVENTION Assembling a fuse according to the present invention includes the following steps:

a. Each of a pair of cylindrical terminal plugs is provided with axially extending bores arranged to form a pattern in the shape of a polygon in each of said pair of terminal plugs.

b. Said pair of terminal plugs is interconnected by a plurality of rods engaging said bores in said pair of terminal plugs, forming a dimensionally stable squirrelcage-like structure by said pair of terminal plugs and said plurality of rods.

c. A fusible element is wound helically around the portions of said plurality of rods situated between the axially inner end surfaces of said pair of terminal plugs and each end of the fusible element is conductively connected to one of the pair of terminal plugs.

d. The squirrel-cage like structure with the fusible element wound around the rods thereof is inserted into a fuse casing and the ends of said casing are affixed to said pair of terminal plugs.

e. Finally the casing is filled with a pulverulent arcquenching filler through an axial aperture in one of the pair of terminal plugs and the plurality of rods is removed from said pair of terminal plugs and from said casing through one of said pair of terminal plugs by exerting an axial pull on said plurality of rods.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are partly diagrammatic side elevations and partly vertical sections of phases of assembling a high-voltage fuse according to the present invention, the center portion of the structure being broken away in both figures;

FIG. 3 shows in the same fashion as FIGS. 1 and 2 a completely assembled fuse;

FIG. la is a section along la-la of FIG. 1;

FIG. 1b is a section along lb-lb of FIG. 1;

FIG. 2a is a section along 2a-2a of FIG. 2;

FIG. 3a is an end view of the structure of FIG. 3 seen in the direction of the arrow 3a of FIG. 3;

FIGS. 4 to 6 show in the same way as FIGS. 1 and 2 a modification of the assembly method shown in FIGS. 1 and 2;

FIG. 4a is a section along 4a-4a of FIG. 4; and

FIG. 5a is a section along 5a5a of FIG. 5.

DESCRIPTION OF PREFERRED METHODS OF ASSEMBLING FUSES In FIG. 1 reference numerals 1, 2 have been applied to indicate a pair of cylindrical terminal plugs. Terminal plug 1 is provided with a central aperture or passageway 3 (see FIG. 2) of relatively large diameter and with four bores or passageways 4 (see FIG. 1a) of relatively small diameter. Terminal plug 2 is provided with four internally screw-threaded bores or passageways 5 of relatively small diameter. Passageways or bores 4 and 5 are arranged to establish a pattern in the shape of a polygon in each of terminal plugs 1 and '2. As shown in FIG. 1 bores or passageways 4 extend from one end surface of terminal plug 1 to the other end surface thereof. The bores or passageways 5 in terminal plug 2 extend preferably from the inner end surface thereof axially outwardly, but not entirely to the opposite or axially outer end surface of terminal plug 2. In other words, bores 5 form blind holes. The axially outer ends of bores or passageways 4 have preferably a larger diameter than the axially inner ends thereof and the axially outer portions of bores or passageways 4 are preferably internaly screw-threaded. The same applies to blind holes 5.

The first step in the assembly process of the fuse shown in FIGS. 1 and 2 consists in interconnecting terminal plugs l, 2 by a plurality of metal rods 6 projecting 'through passageways 4 and engaging passageways 5.

Thus a squirrel-cage-like structure is formed by terminal plugs 1, 2 and metal rods 6. Rods 6 have external screw-threads engaging the internal screw-threads in bores 4 and have external screw-threads engaging the internal screw-threads in blind holes 5. The portions of the surfaces of rods 6 between the screw-threaded portions thereof, or the portions thereof situated between the axially inner end surfaces of plugs 1, 2, are smooth.

In the drawing the bores or passageways 4, 5 are shown to be arranged in such a way as to establish a pattern in the shape of a square in each of terminal plugs l, 2. Passageways or bores 4,5 might be arranged to establish a pattern in the shape of another polygon, e.g., of a pentagom'or of a hexagon, in terminal plugs After combining parts 1, 2 and 6 into a squirrel-cagelike structure fusible element 7 is wound helically around the smooth portions of rods 6 situated between the axially inner end surfaces of plugs l, 2 and the ends of fusible element 6 are conductively connected to terminal plugs 1, 2. This may be achieved in the fashion more fully disclosed in US. Pat. No. 3,571,775 to Frederick J. Kozacka et al., issued March 23, 1971 for HIGH-VOLTAGE FUSE HAVING A PLURALITY OF HELICALLY WOUND RIBBON FUSE LINKS.

The squirrel-cage-like structure 1, 2, 6 of FIG. 1 with the fusible element 7 helically wound thereon is then inserted into a tubular casing 8 of electric insulating material, e.g., melamine glass cloth. This is, in essence, a press-fitting operation which may be performed by means of a hydraulic press. Upon inserting the unit 1, 2, 6, 7 into casing 8 the terminal plugs 1, 2 are secured in position by means of steel pins 9 projecting transversely through casing 8 into terminal plugs 1, 2.

Now the filling process of the fuse may be started. To this end a pulverulent arc-quenching filler such as quartz sand is poured into casing 8 through the bore or passageway 3 in terminal plug 1. The level of the pulverulent arc-quenching filler 10 rises gradually in casing 1, not unlike the level rises in a container which is gradually filled with liquid from the top of the container.

As shown in FIG. 1 the four metal rods 6 may be attached to a common rod support 11. As the level of the arc-quenching filler l0 rises gradually inside of easing 8, the four metal rods 6 may be gradually raised and lifted out of easing 8 by movingrod support 11 in the direction of the arrow R. There is virtually no tendency of any deformation of the fuse link or fusible element 7 during the process of filling casing 8 and withdrawing metal rods 6. Since the increments involved in lifting metal rods 6 may be kept small and since the void formed by raising metal rods 6 is small on account of the size of the increments and on account of the relatively small cross-sectional area of each metal rod 6, and since casing 8 is filled along the axis thereof and the pulverulent filler filled into casing 8 along its axis tends to flow radially outwardly right into the small voids formed by the withdrawal of rods 6. In some instances a slight deformation of the turn of fusible element 7 immediately adjacent to the upper terminal plug 1 may be observed. This deformation may be kept so small as to be negligible. It can completely be avoided by vibrating the entire structure during the filling process in a direction longitudinally thereof and by ram-packing pulverulent arc-quenching filler through passage 3 in terminal plug 1 prior to complete withdrawal of metal rods 6.

It is also possible to fill casing 8 with arc-quenching filler 10 without withdrawing metal rods 6 from the latter and to withdraw metal rods 6 by exerting an axial or longitudinal pull on the latter only after casing 8 has been filled with the arc-quenching filler 10. If metal rods 6 are withdrawn after casing 8 has been filled with arc-quenching filler 10, they may either be withdrawn simultaneously, or sequentially. Both methods result in satisfactory high-voltage fuse structures, though sequential withdrawal of rods 6 lessens the tendency of a deformation of the winding formed by helical fusible element'7. As long as one single fusible element 7 is wound helically around metal rods 6 and its pitch is relatively steep, the case filling and rod withdrawal process is not particularly critical. The filling of casing 8 with a pulverulent arc-quenching filler 10 and withdrawal of metal rods 6 from casing 8 and terminal plugs 1, 2 requires particular care in case that a plurality of fuse links is wound helically around metal rods 6 rather than but one single fuse link because in the former instance the spacing between the several fuse links ought to be rigorously constant. This condition does not allow any deformation of any of the windings of the several fuse links incident to removal of metal rods 6 from casing 8. Removing metal rods 6 sequentially rather than simultaneously, and vibrating the units including terminal plugs 1, 2 and casing 8 in a direction longitudinally of the latter during the removal of metal rods 6 tends to preclude any distortion of the helical fusible elements 7 incident to removal of metal rods 6.

In case that metal rods 6 are removed from casing 8 and plugs l, 2 after casing 8 has been filled with pulverulent arc-quenching filler 10, it is necessary, or desirable, to add some pulverulent arc-quenching filler 10 into casing 3 after removal of metal rods 6 to take care of the small space vacated by their removal.

As mentioned above, the axially outer ends of bores or passageways 4 in terminal plug 1 may be screwthreaded, as indicated at 1". In this case the screwthreaded portion of rods 6 engaging the screw-threads 1 in bores or passageways 4 must be brought out of engagement with screw-threads 1" preparatory to lifting or raising the common rod support 11. This is achieved by turning rods 6 by means of a screw-driver, or other appropriate tool. As a general rule, a highvoltage fuse calls for the provision of a pair of terminal caps or ferrules to connect the fuse into an electric circuit, i.e., to insert a fuse into a fuse holder. The screwthreads 1" provided in terminal plug 1 for maintaining metal rods 6 in position may be used to secure a terminal cap or ferrule 13 to terminal plug 1. This may be achieved by means of a plurality of screws 12 projecting through caps 13 into screw-threads 1' in passageways 4. It will be understood that removal of rods 6 precedes the insertion of screws 12 into the screwthreaded bores vacated by the removal of rods 6, and that the mounting of caps 13 precedes the insertion of screws 12 into terminal plug 1.

FIG. 3 shows a high-voltage fuse which has been made in accordance with the above teachings. Terminal caps 13 have been mounted on both ends of casing 8. The upper cap 13 has been mounted on casing 8 upon filling the latter with pulverulent arc-quenching filler l0 and upon removal of rods 6. Each screw 12 is inserted into one of the screw-threaded bores or passageways 4 previously occupied by one of the four metal rods 6. Prior to mounting ferrules 13 on casing 8 bore or passageway 3 is plugged by a screw-threaded plug 14. The lower ferrule 13 is affixed to lower terminal plug 2 by means of a single hex screw 15.

In the structure shown -in FIGS. 1 and 2 the metal I rods 6 have a dual function in that they form a spacing means for spacing terminal plugs. 1 and 2 for the period of time prior to insertion of the unit 1, 2, 6, 7 into casing 8 and in that they also form a temporary mandrel for fusible element 7 for the period of time prior to filling of casing 8 with pulverulent arc-quenching filler 10. In the structure of FIGS. 4 and 5 the terminal plug spacing function and the fusible element supporting function are effected by two different parts. Plugs l and 2 are originally spaced by a center post 16 having a knurled cylindrical handle 17. The lower portion of center post 16 is cone-shaped and provided with an axial bore 18 and radial slots 19, as a result of which the lower portion of center post 16 is radially flexible. This radially flexible portion of center post 16 is inserted into a recess or blind hole 20 provided in the axially inner end surface of terminal plug 2. The upper portion of center post 16 is screw-threaded and cooperatively engages the internal screw thread in passageway 3 provided in terminal plug 1. The four metal rods 6 inserted into plugs 1, 2 upon spacing thereof by center post 16 serve merely the function of supporting the fusible element 7 temporarily, but not as means for spacing terminal plugs l, 2.

In assembling a fuse structure the first step consists of spacing a pair of terminal plugs l, 2 by means of center post 16. Thereafter metal rods 6 are arranged around center post 16 by inserting the same in screwthreaded satellite bores or passageways 4, 5, thus forming a squirrel-cage-like structure. The center post 16 is removed from said squirrel-cage-like structure upon insertion thereof into casing 8 and prior to filling casing 8 with pulverulent arc-quenching filler 10. Casing 8 is filled with pulverulent arc-quenching filler 10 through the aperture or passageway 3 formed by removal of center post 16. Rods 16 are withdrawn either during the process of filling casing 8 with pulverulent arcquenching filler 10, or after casing 8 has been filled with pulverulent arc-quenching filler 10 and in any case only when ribbon fuse link 7 is sufficiently supported by filler 10.

The same reference numerals have been applied in FIGS. 1 to 3 and in FIGS. 4-6 to indicate like parts, ex-

cept that a prime has been added to the parts of FIGS. 4-6. Therefore FIGS. 4-6 do not call for any comment inasmuch as they illustrate the same process as that illustrated in FIGS. l-3.

FIG. 6 illustrates a sequential rather than a simultaneous removal of metal rods 6. As shown in FIG. 6 two of rods 6 are still in their initial position upon filling casing8' with filler 10, while the third metal rod 6' is in the process of being withdrawn.

FIGS. 1 and 5 illustrate novel sub-assemblys for manufacturing high-voltage fuses. This sub-assembly include a pair of spaced co-axially arranged cylindrical terminal plugs 1, 2 and 1, 2, respectively of which each is provided with registering axially extending satellite bores or passageways 4, 5 and 4', 5, respectively arranged around the common axis of the pair of terminal plugs 1, 2 and l, 2, respectively. The screwthreaded bores 4, 4' in terminal plug 1, l extend all the way from one end surface of terminal plug 1 to the other end surface thereof. A plurality of metal rods 6, 6' is arranged around the common axis of the pair of terminal plugs 1, 2and 1', 2', respectively, and inserted into bores 4, 5; 4, 5 and form jointly with said pair of terminal plugs l, 2 and l, 2', respectively, a squirrelcage-like structure 1, 2, 6 and 1, 2, 6, respectively. A fusible element 7, 7' is wound helically around metal rods 6,6. Each of the ends of fusible element 7, 7' is conductively connected to one of the terminal plugs 1, 2 and l, 2, respectively.

In its preferred form illustrated in FIG. 3 a highvoltage fuse embodying this invention includes a pair of terminal plugs 1,2 closing the ends of a tubular casing 8 of electric insulating material. One of the pair of terminal plugs 1, 2 has a central passageway 3 of relatively large diameter extending axially from one of the end surface of said one 1 of said pair of terminal plugs 1, 2 to the other end surface thereof. Said one 1 of said pair of terminal plugs 1, 2 further has a plurality of internally screw-threaded bores 4 of relatively small diameter spaced equidistantly from the axis of said casing 8 and extending axially from one of the end surfaces of said one 1 of said pair of terminal plugs 1, 2 to the other end surface thereof. The other 2 of said pair of terminal plugs 1, 2 has a plurality of cylindrical internally screwthreaded blind holes or recesses each arranged in coaxial relation to one of said plurality of bores 4 and each extending from the axially inner end surface of said other two of said pair of terminal plugs l, 2 axially outwardly a distance less than the spacings (FIG. 1) between the end surfaces of said other 2 of said pair of terminal plugs 1, 2. The central passageway 3 in terminal plug 1 and the bores 4 in the latter are closed by apl5 propriate closing means. Bores 4 may be closed by screws 12 maintaining terminal cap or ferrule 13 in position. Central bore 3 may be closed by a screw plug 14 or, as an alternative, may be used to accommodate a blown fuse indicator as more fully disclosed in the copending patent application of Richard A. Belcher, filed May 7, 1970, Ser. No. 035,465 for ELECTRIC CAR- TRIDGE FUSE HAVING PLUG TERMINALS, now US. Pat. No. 3,621,433 issued Nov. 6, 1971. The finished fuse includes a helically wound fusible element 7 arranged inside of and in coaxial relation to casing 8. Fusible element 7 conductively interconnects terminal plugs 1, 2 and is supported between the ends thereof solely by the pulverulent arc-quenching filler 10 inside of casing 8. It will be apparent from the foregoing that the length of rods 6 and 6, respectively, should exceed the length of the casing 8 and 8', respectively. In other words, the length of rods 6, 6' should exceed the spacing between the axially inner end surfaces of the pair of plugs 1,2 and 1',2', respectively, plus the length of one of said pair of plugs 1 and 1, respectively. If this condition is met rods 6, 6' will project a distance beyond the axially outer end surfaces of plugs l, 1 sufficient to make it possible to conveniently manipulate rods 6, 6.

I claim as my invention: 1. A method of assembling electric high-voltage fuses including the steps of a. providing each of a pair of cylindrical terminal plugs with axially extending bores circular in crosssection arranged to establish a pattern in the shape of a polygon in each of said pair of terminal plugs;

between the axially inner end surfaces of said pair,

of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs;

inserting the squirrel-cage-like structure formed by said pair of terminal plugs and said plurality of rods with said fusible element thereon into a tubular casing and affixing said pair of terminal plugs to said casing; and thereafter e. filling said casing with a pulverulent arc-quenching filler through a filling aperture in said pair of terminal plugs and removing said plurality of rods from said fusible element and from the space inside said casing through said plurality of bores in said one of said pair of terminal plugs.

2. A method as specified in claim 1 including the steps of a. causing ends of said plurality of rods to project beyond the axially outer end surface of said one of said pair of terminal plugs;

b. affixing to said ends of said plurality of rods projecting beyond said axially outer end surface of said one of said pair of terminal plugs a common rod support; and

c. moving said common rod support relative to said casing in a direction longitudinally thereof to jointly and simultaneously remove all of said plurality of rods from said pair of terminal plugs and from said casing.

3. A method as specified in claim 1 including the steps of a. providing said plurality of bores in said one of said pair of terminal plugs with internal screw-threads;

b. providing each of said plurality of rods with an external screw-thread and screwing by means thereof each of said plurality of rods .into one of said plurality of internally screw-threaded bores;

c. mounting a terminal cap upon said casing and upon said one of said pair of terminal plugs upon filling said casing with said pulverulent arcquenching filler and removal of said plurality of rods; and

d. securing said terminal cap to said one of said pair of terminal plugs by a plurality of screws each engaging said internal screw-threads in said plurality of bores of said one of said pair of terminal plugs.

4. A method as specified in claim 1 including the steps of a. spacing said pair of terminal plugs by a center post;

b. arranging said plurality or rods around said center post;

c. removing said center post upon insertion of said squirrel-cage-like structure into said casing and prior to filling said casing with said pulverulent arcquenching filler; and

d. thereafter filling said casing with said pulverulent arc-quenching filler through a central passageway established by removal of said center post.

5. A method as specified in claim 1 including the steps of a. removing said plurality of rods sequentially from said pair of terminal plugs and from said casing; and

b. vibrating said pair of terminal plugs and said casing in a direction longitudinally of said casing during removal of said plurality of rods therefrom.

6. A method of assembling electric high-voltage fuses including the steps of a. providing one of a pair of cylindrical terminal plugs with a plurality of axial passageway bores extend-' ing between the end surfaces thereof, and providing the other of said pair of cylindrical terminal plugs with a plurality of axially extending blind bores;

b. interconnecting said pair of terminal plugs by a plurality of rods by inserting one end of each of said plurality of rods into one of said plurality of passageway bores and by inserting the other end of each of said plurality of rods into one of said plurality of blind bores in said other of said pair of terminal plugs, and spacing said pair of terminal plugs a smaller distance than the length of said plurality of rods to form a squirrel-cage-like structure with one end of each of said plurality of rods projecting in axial direction from the axially outer end surface of said one of said pair of terminal plugs;

c. winding a fusible element helically around the portion of said plurality of rods situated between said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs;

d. press-fitting said pair of terminal plugs into a tubular casing of insulating material; and

e. filling said casing with a pulverulent arc-quenching filler through a centrally located axial aperture in said one of said pair of terminal plugs and withdrawing said plurality of rods from said fusible element and from said casing through said passageway bores in said one of said pair of terminal plugs by exerting an axial pull on said one end of each of said plurality of rods projecting from said axially outer end surface of said one of said pair of terminal plugs.

7. A sub-assembly for making high-voltage fuses including a. a pair of spaced coaxially arranged cylindrical terminal plugs, each of said pair of terminal plugs being provided with registering axially extending bores arranged around the common axis of said pair of terminal plugs, said bores of at least one of said pair of terminal plugs extending all the way from one end surface thereof to the other end surface thereof;

b a plurality of metal rods arranged around the common axis of said pair of terminal plugs and being inserted into said bores of said pair of terminal plugs and forming jointly with said pair of terminal plugs a substantially squirrel-cage-shaped structure, the length of each of said plurality of rods exceeding the sum of the spacing between the axially inner end surfaces of said pair of terminal plugs plus the thickness of one of said pair of terminal plugs so that said plurality of rods extends beyond the axially outerend surface of said one of said pair of terminal plugs; and

c. a fusible element wound helically around said plurality of metal rods and having ends each conductively connected to one of said pair of terminal plugs.

8. A sub-assembly as specified in claim 7 wherein a. one of said pair of terminal plugs is provided in the center thereof with a screw-threaded bore having a substantially larger diameter than said bores arranged around the common axis of said pair of terminal plugs; and wherein b. said screw-threaded bore in said one of said pair of terminal plugs positions a center post arranged inside of an surrounded by said plurality of metal rods.

*9. A high-voltage fuse including a. a tubular casing of electric insulating material;

b. a pair of terminal plugs closing the ends of said casing, one of said pair of terminal plugs having a central passageway of relatively large diameter extending axially from one of the end surfaces of said one of said pair of terminal plugs to the other end surface thereof, said one of said pair of terminal plugs further having a plurality of bores of relatively small diameter spaced equidistantly from the axis of said casing and extending axially from one of the end surfaces of said one of said pair of terminal plugs to the other end surface thereof, the other of said pair of terminal plugs having-a plurality of internally screw-threaded blind bores each arranged in coaxial relation to one of said plurality of bores and each extending from the axially inner end surface of said other of said pair of terminal plugs axially outwardly a distance less than the spacing between the end surfaces of said other of said pair of terminal plugs;

c. a pulverulent arc-quenching filler inside said casd. means for closing said central passageway and said plurality of bores to preclude escape of said arequenching filler from said casing; and I e. a helically wound fusible element arranged inside of, and in coaxial relation to, said casing conductively interconnecting said pair of terminal plugs, said fusible element being supported between the ends thereof solely by said pulverulent arcquenching filler.

10. A method of assembling electric fuses including the steps of a. providing one of a pair of terminal plugs with a plurality of axial internally screw-threaded bores extending from one end surface to the other end surface thereof and arranged to form a pattern in the shape of a polygon;

b. providing the other of said pair of terminal plugs with a plurality of axial internally screw-threaded blind holes arranged to form said pattern in the shape of a polygon;

c. fixedly spacing said pair of terminal plugs by means of a plurality of externally screw-threaded rods by screwing one screw-threaded end of each of said plurality of rods into one of said plurality of bores and by screwing another screw-threaded end of each of said plurality of rods into one of said plurality of blind holes;

d. winding a fusible element in ribbon form substantially helically around the portions of said plurality of rods situated between the axially inner end surfacesof said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs;

e. inserting the structure formed by said pair of terminal plugs and said plurality of rods with said fusible element thereon into a tubular casing and affixing said pair of terminal plugs to said casing; and

f. thereafter filling said casing with a pulverulent arcquenching filler through a filling aperture in one of said pair of terminal plugs and removing said plurality of rods from said fusible element by first unscrewing said plurality of rods and then lifting said plurality of rods out of said casing through said plurality of bores in said one of a pair of terminal plugs.

11. A method of assembling electricfuses including the steps of i a. providing one of a pair of terminal plugs with a relatively large center bore and with a plurality of relatively small satellite bores surrounding said center bore, said center bore and said plurality of satellite bores extending all the way through said one of said pair of terminal plugs;

b. providing the other of said pair of terminal plugs with a relatively large center blind hole and with a plurality of relatively small satellite blind holes surrounding said center blind hole;

c. spacing said pair of terminal plugs a predetermined distance by inserting a center post into said center bore and into said center blind hole;

d. inserting a plurality of rods into said plurality of satellite bores and into said plurality of satellite blind holes to form a squirrel-cage-like structure;

e. winding a fusible element substantially helically around the portions of said plurality of rods situated between the axially inner end surfaces of said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs;

f. inserting said squirrel-cage-like structure with said fusible element thereon in coaxial relation into a tubular casing and affixing said pair of terminal plugs to said casing;

g. removing said center post so as to open said center bore in said one of said pair of terminal plugs; and

h. thereafter filling said casing through said center bore in said one of said pair of terminal plugs with a pulverulent arc-quenching filler and removing said plurality of rods from said fusible element through said plurality of satellite bores in said one of said pair of terminal plugs.

12. A method for assembling electric fuses including the steps of a. providing one of a pair of cylindrical terminal plugs with a plurality of bores extending from one end surface of said one of said pair of terminal plugs to the other end surface thereof;

b. providing the other of said pair of terminal plugs with a plurality of blind holes forming the same pattern as said plurality of bores in said one of said pair of terminal plugs;

c. arranging said pair of terminal plugs in coaxial relation in such a way that each of said plurality of bores registers with one of said plurality of blind holes;

(1'. threading a plurality of rods through said plurality of bores in said one of said pair of terminal plugs into engagement with said plurality of blind holes in said other of said pair of terminal plugs and affixing said plurality of rods to said pair of terminal plugs in such a way that one of the ends of each of said plurality of rods project axially outwardly beyond the axially outer end surface of said one of said pair of terminal plugs;

e. winding a fusible ribbon element substantially heli- 6 cally around the portions of said plurality of rods situated between the axially inner end surfaces of said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs;

f. inserting said pair of terminal plugs into a tubular casing having a shorter length than the length of said plurality of rods so that ends of said plurality of rods project beyond said casing;

g. pinning said casing to said pair of terminal plugs;

and

h. thereafter filling said casing with a pulverulent arcquenching filler through a filler aperture in said pair of terminal plugs and sequentially removing said plurality of rods from said fusible element by sequentially lifting said ends of said plurality of rods projecting beyond said casing.

13. A method of assembling electric fuses including the steps of v a. providing one of a pair of terminal plugs with a plurality of bores extending from one end surface to the other end surface thereof and having internal screw-threads extending at least along a portion of the length of each of said plurality of bores;

b. providing the other of said pair of terminal plugs with a plurality of internally screw-threaded blind holes forming the same pattern as said plurality of bores in said one of said pair of terminal plugs;

c. spacing said pair of terminal plugs by means of a plurality of rods each having externally screw threaded spaced portions and each having a nonscrew-threaded portion intermediate said screwthreaded spaced portions by screwing said screwthreaded portions of said plurality of rods into said internal screw-threads of said plurality of bores in said one of said pair of terminal plugs and into said plurality of internally screw-threaded blind holes in said other of said pair of terminal plugs;

winding a fusible ribbon element substantially helically around said non-screw-threaded portion of each of said plurality of rods and conductively connecting each end of said fusible element to one of said pair of terminal plugs;

. inserting said pair of terminal plugs into a tubular casing and affixing said casing to said pair of terminal plugs so as to preclude relative movement between said pair of terminal plugs and said casing; and

f. filling said casing with a pulverulent arc-quenching filler through a filling aperture in one of said pair of terminal plugs and removing said plurality of rods from said fusible element by first unscrewing said plurality of rods from said pair of terminal plugs and by thereafter pulling said plurality of rods out of said casing through said plurality of bores in said one of a pair of terminal plugs.

14. A method for assembling electric fuses including the steps of a. moving each of a plurality of rods through a plurality of bores provided in a plug terminal in such a way that both ends of each of said plurality of rods project in opposite directions from the end surfaces of said plug terminal;

b. inserting one end of each of said plurality of rods into one of a plurality of blind bores provided in another plug terminal;

c. winding a fusible ribbon substantially helically around the portions of said plurality of rods positioned between said plug terminal and said another plug terminal and conductively connecting the 13 14 ends of said fusible ribbon to said plug terminal and rods in bores of said pair of terminal plugs; to said another plug terminal; c. winding a fusible ribbon substantially helically d. plugging both ends of a tubular casing by said plug around said plurality of rods and conductively conterrninal and said another plug terminal and allownecting the ends of said fusible ribbon to said pair ing portions of said plurality of rods to project outof plug terminals; side said casing; and d. inserting said pair of plug terminals, said center e. thereafter filling a pulverulent arc-quenching filler post and said plurality of rods with said fusible ribthrough an aperture in said plug terminal into said bon thereon into a tubular casing and affixing said casing and withdrawing said plurality of rods from casing to said pair of plug terminals; said fusible ribbon when said fusible ribbon is sube. removing said center post from said pair of plug stantially supported by said pulverulent arcterminals and from said casing; quenching filler by lifting said portions of said pluf. filling said casing with a pulverulent arc-quenching rality of rods projecting outside said casing. filler through an aperture established by removal of 15. A method of assembling electric fuses including said center post; and the steps of 5 g. withdrawing said plurality of rods from said fusible a. spacing a pair of plug terminals by a removable ribbon through said bores in said pair of plug termicenter post; nals when said fusible ribbon is substantially supb. surrounding said center post by a plurality of reported by said pulverulent arc-quenching filler.

movable rods and affixing points of said plurality of 

1. A method of assembling electric high-voltage fuses including the steps of a. providing each of a pair of cylindrical terminal plugs with axially extending bores circular in cross-section arranged to establish a pattern in the shape of a polygon in each of said pair of terminal plugs; b. threading a plurality of rods through said plurality of bores in one of said pair of terminal plugs, establishing firm engagement of the ends of said plurality of rods remote from said one of said pair of terminal plugs inside said plurality of bores in the other of said pair of terminal plugs and maintaining a fixed spacing between said pair of terminal plugs by means of said plurality of rods; c. winding a fusible element substantially helically around the portion of said plurality of rods situated between the axially inner end surfaces of said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs; d. inserting the squirrel-cage-like structure formed by said pair of terminal plugs and said plurality of rods with said fusible element thereon into a tubular casing and affixing said pair of terminal plugs to said casing; and thereafter e. filling said casing with a pulverulent arc-quenching filler through a filling aperture in said pair of terminal plugs and removing said plurality of rods from said fusible element and from the space inside said casing through said plurality of bores in said one of said pair of terminal plugs.
 2. A method as specified in claim 1 including the steps of a. causing ends of said plurality of rods to project beyond the axially outer end surface of said one of said pair of terminal plugs; b. affixing to said ends of said plurality of rods projecting beyond said axially outer end surface of said one of said pair of terminal plugs a common rod support; and c. moving said common rod support relative to said casing in a direction longitudinally thereof to jointly and simultaneously remove all of said plurality of rods from said pair of terminal plugs and from said casing.
 3. A method as specified in claim 1 including the steps of a. providing said plurality of bores in said one of said pair of terminal plugs with internal screw-threads; b. providing each of said plurality of rods with an external screw-thread and screwing by means thereof each of said plurality of rods into one of said plurality of internally screw-threaded bores; c. mounting a terminal cap upon said casing and upon said one of said pair of terminal plugs upon filling said casing with said pulverulent arc-quenching filler and removal of said plurality of rods; and d. securing said terminal cap to said one of said pair of terminal plugs by a plurality of screws each engaging said internal screw-threads in said plurality of bores of said one of said pair of terminal plugs.
 4. A method as specified in claim 1 including the steps of a. spacing said pair of terminal plugs by a center post; b. arranging said plurality or rods around said center post; c. removing said center post upon insertion of said squirrel-cage-like structure into said casing and prior to filling said casing with said pulverulent arc-quenching filler; and d. thereafter filling said casing with said pulverulent arc-quenching filler through a central passageway established by removal of said center post.
 5. A method as specified in claim 1 including the steps of a. removing said plurality of rods sequentially from said pair of terminal plugs and from said casing; and b. vibrating said pair of terminal plugs and said caSing in a direction longitudinally of said casing during removal of said plurality of rods therefrom.
 6. A method of assembling electric high-voltage fuses including the steps of a. providing one of a pair of cylindrical terminal plugs with a plurality of axial passageway bores extending between the end surfaces thereof, and providing the other of said pair of cylindrical terminal plugs with a plurality of axially extending blind bores; b. interconnecting said pair of terminal plugs by a plurality of rods by inserting one end of each of said plurality of rods into one of said plurality of passageway bores and by inserting the other end of each of said plurality of rods into one of said plurality of blind bores in said other of said pair of terminal plugs, and spacing said pair of terminal plugs a smaller distance than the length of said plurality of rods to form a squirrel-cage-like structure with one end of each of said plurality of rods projecting in axial direction from the axially outer end surface of said one of said pair of terminal plugs; c. winding a fusible element helically around the portion of said plurality of rods situated between said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs; d. press-fitting said pair of terminal plugs into a tubular casing of insulating material; and e. filling said casing with a pulverulent arc-quenching filler through a centrally located axial aperture in said one of said pair of terminal plugs and withdrawing said plurality of rods from said fusible element and from said casing through said passageway bores in said one of said pair of terminal plugs by exerting an axial pull on said one end of each of said plurality of rods projecting from said axially outer end surface of said one of said pair of terminal plugs.
 7. A sub-assembly for making high-voltage fuses including a. a pair of spaced coaxially arranged cylindrical terminal plugs, each of said pair of terminal plugs being provided with registering axially extending bores arranged around the common axis of said pair of terminal plugs, said bores of at least one of said pair of terminal plugs extending all the way from one end surface thereof to the other end surface thereof; b. a plurality of metal rods arranged around the common axis of said pair of terminal plugs and being inserted into said bores of said pair of terminal plugs and forming jointly with said pair of terminal plugs a substantially squirrel-cage-shaped structure, the length of each of said plurality of rods exceeding the sum of the spacing between the axially inner end surfaces of said pair of terminal plugs plus the thickness of one of said pair of terminal plugs so that said plurality of rods extends beyond the axially outer end surface of said one of said pair of terminal plugs; and c. a fusible element wound helically around said plurality of metal rods and having ends each conductively connected to one of said pair of terminal plugs.
 8. A sub-assembly as specified in claim 7 wherein a. one of said pair of terminal plugs is provided in the center thereof with a screw-threaded bore having a substantially larger diameter than said bores arranged around the common axis of said pair of terminal plugs; and wherein b. said screw-threaded bore in said one of said pair of terminal plugs positions a center post arranged inside of an surrounded by said plurality of metal rods.
 9. A high-voltage fuse including a. a tubular casing of electric insulating material; b. a pair of terminal plugs closing the ends of said casing, one of said pair of terminal plugs having a central passageway of relatively large diameter extending axially from one of the end surfaces of said one of said pair of terminal plugs to the other end surface thereof, said one of said pair of terminal plugs further having a plurality of bores of relatively small diameter spaced equidistantly from the axis of sAid casing and extending axially from one of the end surfaces of said one of said pair of terminal plugs to the other end surface thereof, the other of said pair of terminal plugs having a plurality of internally screw-threaded blind bores each arranged in coaxial relation to one of said plurality of bores and each extending from the axially inner end surface of said other of said pair of terminal plugs axially outwardly a distance less than the spacing between the end surfaces of said other of said pair of terminal plugs; c. a pulverulent arc-quenching filler inside said casing; d. means for closing said central passageway and said plurality of bores to preclude escape of said arc-quenching filler from said casing; and e. a helically wound fusible element arranged inside of, and in coaxial relation to, said casing conductively interconnecting said pair of terminal plugs, said fusible element being supported between the ends thereof solely by said pulverulent arc-quenching filler.
 10. A method of assembling electric fuses including the steps of a. providing one of a pair of terminal plugs with a plurality of axial internally screw-threaded bores extending from one end surface to the other end surface thereof and arranged to form a pattern in the shape of a polygon; b. providing the other of said pair of terminal plugs with a plurality of axial internally screw-threaded blind holes arranged to form said pattern in the shape of a polygon; c. fixedly spacing said pair of terminal plugs by means of a plurality of externally screw-threaded rods by screwing one screw-threaded end of each of said plurality of rods into one of said plurality of bores and by screwing another screw-threaded end of each of said plurality of rods into one of said plurality of blind holes; d. winding a fusible element in ribbon form substantially helically around the portions of said plurality of rods situated between the axially inner end surfaces of said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs; e. inserting the structure formed by said pair of terminal plugs and said plurality of rods with said fusible element thereon into a tubular casing and affixing said pair of terminal plugs to said casing; and f. thereafter filling said casing with a pulverulent arc-quenching filler through a filling aperture in one of said pair of terminal plugs and removing said plurality of rods from said fusible element by first unscrewing said plurality of rods and then lifting said plurality of rods out of said casing through said plurality of bores in said one of a pair of terminal plugs.
 11. A method of assembling electric fuses including the steps of a. providing one of a pair of terminal plugs with a relatively large center bore and with a plurality of relatively small satellite bores surrounding said center bore, said center bore and said plurality of satellite bores extending all the way through said one of said pair of terminal plugs; b. providing the other of said pair of terminal plugs with a relatively large center blind hole and with a plurality of relatively small satellite blind holes surrounding said center blind hole; c. spacing said pair of terminal plugs a predetermined distance by inserting a center post into said center bore and into said center blind hole; d. inserting a plurality of rods into said plurality of satellite bores and into said plurality of satellite blind holes to form a squirrel-cage-like structure; e. winding a fusible element substantially helically around the portions of said plurality of rods situated between the axially inner end surfaces of said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs; f. inserting said squirrel-cage-like structure with said fusible element thereon in coaxial relation into a tubular casing and affixing said pair of terminal plugs to Said casing; g. removing said center post so as to open said center bore in said one of said pair of terminal plugs; and h. thereafter filling said casing through said center bore in said one of said pair of terminal plugs with a pulverulent arc-quenching filler and removing said plurality of rods from said fusible element through said plurality of satellite bores in said one of said pair of terminal plugs.
 12. A method for assembling electric fuses including the steps of a. providing one of a pair of cylindrical terminal plugs with a plurality of bores extending from one end surface of said one of said pair of terminal plugs to the other end surface thereof; b. providing the other of said pair of terminal plugs with a plurality of blind holes forming the same pattern as said plurality of bores in said one of said pair of terminal plugs; c. arranging said pair of terminal plugs in coaxial relation in such a way that each of said plurality of bores registers with one of said plurality of blind holes; d. threading a plurality of rods through said plurality of bores in said one of said pair of terminal plugs into engagement with said plurality of blind holes in said other of said pair of terminal plugs and affixing said plurality of rods to said pair of terminal plugs in such a way that one of the ends of each of said plurality of rods project axially outwardly beyond the axially outer end surface of said one of said pair of terminal plugs; e. winding a fusible ribbon element substantially helically around the portions of said plurality of rods situated between the axially inner end surfaces of said pair of terminal plugs and conductively connecting each end of said fusible element to one of said pair of terminal plugs; f. inserting said pair of terminal plugs into a tubular casing having a shorter length than the length of said plurality of rods so that ends of said plurality of rods project beyond said casing; g. pinning said casing to said pair of terminal plugs; and h. thereafter filling said casing with a pulverulent arc-quenching filler through a filler aperture in said pair of terminal plugs and sequentially removing said plurality of rods from said fusible element by sequentially lifting said ends of said plurality of rods projecting beyond said casing.
 13. A method of assembling electric fuses including the steps of a. providing one of a pair of terminal plugs with a plurality of bores extending from one end surface to the other end surface thereof and having internal screw-threads extending at least along a portion of the length of each of said plurality of bores; b. providing the other of said pair of terminal plugs with a plurality of internally screw-threaded blind holes forming the same pattern as said plurality of bores in said one of said pair of terminal plugs; c. spacing said pair of terminal plugs by means of a plurality of rods each having externally screw-threaded spaced portions and each having a non-screw-threaded portion intermediate said screw-threaded spaced portions by screwing said screw-threaded portions of said plurality of rods into said internal screw-threads of said plurality of bores in said one of said pair of terminal plugs and into said plurality of internally screw-threaded blind holes in said other of said pair of terminal plugs; d. winding a fusible ribbon element substantially helically around said non-screw-threaded portion of each of said plurality of rods and conductively connecting each end of said fusible element to one of said pair of terminal plugs; e. inserting said pair of terminal plugs into a tubular casing and affixing said casing to said pair of terminal plugs so as to preclude relative movement between said pair of terminal plugs and said casing; and f. filling said casing with a pulverulent arc-quenching filler through a filling aperture in one of said pair of terminal plugs and removing said plurality of rods from said fusible element by first Unscrewing said plurality of rods from said pair of terminal plugs and by thereafter pulling said plurality of rods out of said casing through said plurality of bores in said one of a pair of terminal plugs.
 14. A method for assembling electric fuses including the steps of a. moving each of a plurality of rods through a plurality of bores provided in a plug terminal in such a way that both ends of each of said plurality of rods project in opposite directions from the end surfaces of said plug terminal; b. inserting one end of each of said plurality of rods into one of a plurality of blind bores provided in another plug terminal; c. winding a fusible ribbon substantially helically around the portions of said plurality of rods positioned between said plug terminal and said another plug terminal and conductively connecting the ends of said fusible ribbon to said plug terminal and to said another plug terminal; d. plugging both ends of a tubular casing by said plug terminal and said another plug terminal and allowing portions of said plurality of rods to project outside said casing; and e. thereafter filling a pulverulent arc-quenching filler through an aperture in said plug terminal into said casing and withdrawing said plurality of rods from said fusible ribbon when said fusible ribbon is substantially supported by said pulverulent arc-quenching filler by lifting said portions of said plurality of rods projecting outside said casing.
 15. A method of assembling electric fuses including the steps of a. spacing a pair of plug terminals by a removable center post; b. surrounding said center post by a plurality of removable rods and affixing points of said plurality of rods in bores of said pair of terminal plugs; c. winding a fusible ribbon substantially helically around said plurality of rods and conductively connecting the ends of said fusible ribbon to said pair of plug terminals; d. inserting said pair of plug terminals, said center post and said plurality of rods with said fusible ribbon thereon into a tubular casing and affixing said casing to said pair of plug terminals; e. removing said center post from said pair of plug terminals and from said casing; f. filling said casing with a pulverulent arc-quenching filler through an aperture established by removal of said center post; and g. withdrawing said plurality of rods from said fusible ribbon through said bores in said pair of plug terminals when said fusible ribbon is substantially supported by said pulverulent arc-quenching filler. 